The present disclosure is directed to a pipeline pig for use in cleaning the interior wall of a pipeline. In the present disclosure, a pipeline pig is set forth which incorporates an elongate cylindrical body having a bullet shaped nose at one end and having a transverse back wall at the opposite end. Between the two ends, there is an elongate cylindrical foam body. The foam body is made of a controllable weight of foam material. This provides a pig which has sufficient rigidity to ordinarily extend fully across the circular cross section of a pipe. Even though it is circular, the pig will deform when passing through elbows, valves, reducer nipples, and other changes in pipe size. Because of this construction, the pig is able to traverse any length of pipeline, and to also travel through all the obstructions that are encountered in typical pipeline construction for the express purpose of providing a pig body which deforms sufficiently that a seal is maintained as it travels.
The pig of the present disclosure is especially effective in wiping the pipeline on the interior surface. It forms a seal fully around the pig in contact with the pipeline to reduce leakage. The pig is provided with a transverse back end which is circular in shape and which has a finite thickness so that the circular back end of the pig is able to maintain an effective seal. Because this is provided, the pig is then able to travel with minimal leakage around the pig. Not only that, the pig is constructed with a set of strips on it, the strips including a plurality of scraper blades. The scraper blades are provided with a requisite amount of hardness so that the scraper blades drag on the sidewall and dislodge material from the sidewall. This is especially important in keeping a pipeline clear and free of sidewall coating materials. Consider a natural gas pipeline. In theory, it carries only gas in form, but as a practical matter, a number of gaseous components may liquefy or solidify. For instance, on a hot summer day, it not uncommon for the pipeline to carry a flow of natural gas with some water vapor in it, and certain molecules which will condense in regions of the pipeline where there is a significant temperature drop. On a hot summer day, such a pipeline flow may partially condense which will form in the pipe where the pipe passes under a river or other body of water. The river provides substantial cooling, and the cooling may readily create a large quantity of water condensation. This usually has the form of droplets which collect on the wall of the pipe. If the droplets are sufficiently numerous or large, they will trickle to the bottom of the pipe and will puddle along the bottom of the pipe. If the pipeline is built over valleys and hills, the puddle along the pipeline will trickle downhill and will ultimately collect in the valley of the pipeline, and can be in sufficient quantity that a water trap is accumulated in that region. Liquids formed by condensation are pushed through the pipeline and cleared from the pipeline by pigging the pipeline periodically.
Some of the liquids which condense in a pipeline are heavier molecules which means that they collect on the wall of the pipe and can form various thicknesses and hardnesses of a wall coating. In effect, a paraffin or wax accumulation is built. If that occurs, it sticks and become hardened as the lighter molecules evaporate out of the coating, thereby leaving a very heavy coating if not removed quickly. In summary, both water and oil base molecules can condense and create substantial problems after condensation if not removed periodically. The foregoing problem has been recognized in the past and pipeline pigs have been inserted into pipelines to enable pig removal of the deposits. Moreover, pipeline pigs with scraping surfaces or edges on them have been used in the past. There is a balance between the amount of scraping and the amount of sealing which is implemented to prevent or minimize leakage around the pig. Consider as an example a pipeline pig with a transverse scraper edge which is oversized and unduly stiff. The pig can either stall or wear away rapidly while the scraping edge is destroyed. There is a balance between the amount of stiffness, the amount of contact of the scraping edge with the wall of the pipe, and the amount of leakage by the scraping edges between the pipe and the pig.
The present disclosure sets forth an apparatus which can be installed in a pipeline for scraping and which is able to fully, completely, and controllably clear the pipeline. It is obtained by fabricating an elongate cylindrical pipeline pig which has a transverse back end with a planar face. The planar back face enables the pig to be used with a minimum of leakage by the pig. Such a pig will ordinarily suffice for cleaning a few miles of pipe. Pigs of this construction have been reinforced in the past by adding spiral strips of various abrasive materials. While they may suffer the bulk of the wear in traversing the pipeline, such spiral strips have sometimes been either too stiff or not stiff enough in light of the amount of scraping area provided by the spiral strips. The present applicant has provided such devices and they have worked quite well in the past. There are instances where the nature of the condensate in the pipeline changes so that a different measure of abrasion is desired. Strips have been provided in the past which have been equipped with wire bristles and tungsten carbide particles which scrape or scratch. In all such instances, while devices were successful, they do not necessarily find application for every pipeline pig cleaning operation. The present disclosure sets forth an improved pipeline pig constructed with between one and three spiral strips. While four can be included, the cost of fabrication is reduced by limiting the number typically to the range of one, two or three. One strip is less desirable than two or three strips because it is highly desirable that a every portion of the pipeline pig at any point around the circle of the pig body provide at least two scraping strips. Scraping edges are defined as those edges supported on the pig body and which provide scraping on the pipe. It is desirable that, at any point around the circumference, two strips present scraping edges. The scraping edges are deployed in strips which are set at an angle. By changing the helix angle of the strips mounted on the pig body, and by further changing the angle so that scraper edges on each strip are appropriately positioned with respect to the center line axis of the pig, it is possible to define a pipeline pig having multiple pipeline strips mounted thereon, thereby assuring that the strips provide a specified minimum of scraping edges. More specifically, the strips in the preferred embodiment are constructed with a scraping edge angled at 45.degree. with regard to the strip. If the strip is then mounted at a 45.degree. helix angel of the pig body, the scraping edges are deployed at right angles to the center line axis of the pig. If this is accomplished and there are multiple strips around so that the strips provide at least two strips at a given circumferential location, then the provision of the two strips assures adequate scraping by transversely positioned scraping edges.
Devises of this sort have been attempted heretofore. Two examples are found in the earlier Knapp U.S. Pat. No. 3,204,274 and also U.S. Pat. No. 3,389,417. These two issued patents involving the present inventor are appropriately noted. In addition, a more recent patent issued on Jan. 31, 1995 and is U.S. Pat. No. 5,384,929. These patents show various and sundry aspects of spiral strips. The spiral strips are useful and valuable in many aspects but the present disclosure sets forth improvements over the construction shown in those references. The disclosed construction has advantages which will be detailed hereinafter.